Rubber composition and pneumatic tire

Abstract

Provided are a rubber composition having good fuel economy and good rubber strength while maintaining good appearance, and a pneumatic tire formed from the rubber composition. The rubber composition contains: a rubber component including a diene rubber; a reinforcing filler; and a glycerol fatty acid triester of plant origin. The diene rubber includes an isoprene-based rubber. The glycerol fatty acid triester has a content of saturated fatty acids of 10 to 25% by mass and a content of monovalent unsaturated fatty acids having one unsaturated bond of less than 50% by mass, each based on 100% by mass of the constituent fatty acids of the triester. The reinforcing filler is present in an amount of 50 parts by mass or less per 100 parts by mass of the rubber component.

1 . A rubber composition, comprising:
 a rubber component including a diene rubber;   a reinforcing filler; and   a glycerol fatty acid triester of plant origin,   the diene rubber including an isoprene-based rubber,   the glycerol fatty acid triester having a content of saturated fatty acids of 10 to 25% by mass and a content of monovalent unsaturated fatty acids having one unsaturated bond of less than 50% by mass, each based on 100% by mass of constituent fatty acids of the triester,   the reinforcing filler being present in an amount of 50 parts by mass or less per 100 parts by mass of the rubber component.   
     
     
         2 . The rubber composition according to  claim 1 ,
 wherein the glycerol fatty acid triester has a content of polyvalent unsaturated fatty acids having two or more unsaturated bonds of 50% by mass or more based on 100% by mass of the constituent fatty acids.   
     
     
         3 . The rubber composition according to  claim 1 ,
 wherein the glycerol fatty acid triester satisfies the following relationship (A):
   80≤the content (% by mass) of monovalent unsaturated fatty acids having one unsaturated bond based on 100% by mass of the constituent fatty acids×1(the number of unsaturated bonds)
 
   +the content (% by mass) of divalent unsaturated fatty acids having two unsaturated bonds based on 100% by mass of the constituent fatty acids×2(the number of unsaturated bonds)
 
   +the content (% by mass) of trivalent unsaturated fatty acids having three unsaturated bonds based on 100% by mass of the constituent fatty acids×3(the number of unsaturated bonds)≤200.
 
   
     
     
         4 . The rubber composition according to  claim 1 ,
 wherein the rubber composition comprises 2 to 20 parts by mass of the glycerol fatty acid triester per 100 parts by mass of the rubber component.   
     
     
         5 . The rubber composition according to  claim 1 ,
 wherein the rubber component includes, based on 100% by mass thereof, at least 5% by mass of a copolymer, the copolymer being synthesized by copolymerizing a conjugated diene monomer with a compound represented by the following Formula (1):   
       
         
           
           
               
               
           
         
       
       wherein R 11  and R 12  are the same or different and each denote a hydrogen atom or a C1-C30 hydrocarbon group. 
     
     
         6 . The rubber composition according to  claim 5 ,
 wherein the copolymer comprises, based on 100% by mass of structural units thereof, 5 to 95% by mass of units derived from the conjugated diene monomer and 5 to 95% by mass of units derived from the compound of Formula (1).   
     
     
         7 . The rubber composition according to  claim 1 ,
 wherein the rubber composition exhibits the maximum loss tangent (tan δ) at −46° C. or lower in a temperature dependence curve of tan δ measured at a strain amplitude of ±0.25%, and has a ratio of a loss tangent (tan δ at 20° C.) measured at 20° C. and a strain amplitude of ±0.25% to a loss tangent (tan δ at 0° C.) measured at 0° C. and a strain amplitude of ±0.25% that satisfies the following relationship (X):
   tan δ at 20° C./tan δ at 0° C.≥0.80.
 
   
     
     
         8 . The rubber composition according to  claim 1 ,
 wherein the reinforcing filler includes carbon black and a microfibrillated plant fiber.   
     
     
         9 . The rubber composition according to  claim 1 , which is a rubber composition for tires. 
     
     
         10 . A pneumatic tire, comprising a sidewall formed from the rubber composition according to  claim 1 .